bpo-37268: test_parser fails when run with -Werror (GH-15183)

Use warnings.filterwarnings() when importing the deprecated parser
module.

@pablogsal 


https://bugs.python.org/issue37268



Automerge-Triggered-By: @pablogsal

Lib/test/test_parser.py

 import copy
-import parser
+import warnings
+with warnings.catch_warnings():
+    warnings.filterwarnings('ignore', 'The parser module is deprecated',
+                            DeprecationWarning)
+    import parser
 import pickle
 import unittest
 import operator